Abstract:
As part of the U. S. EPA's effort to develop and demonstrate a reliable model of atmospheric dispersion for pollutant emissions in irregular mountainous terrain, the Complex Terrain Model Development Program was initiated. The first phase, a comprehensive tracer field study, was carried out on Cinder Cone Butte, Idaho during the autumn of 1980. In October 1982, another field experiment, Small ... Hill Impaction Study No.2, was conducted along a 1.5-km section of the Hogback Ridge near Farmington, New Mexico to extend the data base to include flow and dispersion around a two-dimensional ridge. Studies 3 and 4 were located at the Tracy Power Plant near Reno, Nevada and were designed as realistic, full scale plume studies with a tracer gas released through the smokestack of an active power plant.

Tracer study 3 in November 1983 was designed as a modest feasibility study for the more comprehensive fourth study, but enough useful meteorological and tracer data were collected to be included with the fourth study, designated the Full Scale Plume Study conducted in August 1984. The power plant was maintained in warm stand-by condition as SF6 tracer gas and oil-fog were injected into the base of a 91.4-m smokestack. Also, CF3Br tracer gas was released from one of three levels on a 150-m tower located 1.2 km east of the plant and up-wind from the targeted terrain. Meteorological data recorded on the 150-m tower included wind components from tri-axial propeller anemometers at six levels, cup and vane anemometers at three levels, sonic anemometers at three levels and temperature sensors at six levels. Two vertical doppler acoustic sounding systems were operated near the stack and in the valley, and tethersonde soundings were flown near the 150-m tower to compliment data from the tower and doppler systems.

Tracer samples were collected at 110 sites in the surrounding terrain. Concentrations were determined by gas chromatographic analysis. The Full Scale Plume Study comprised 14 experiments from August 6 to 27, 1984 for a total of 128 hours of data collection, mainly during late evening or early morning hours. A tracer concentration data base of over 11,000 hourly samples was accumulated for both tracer gases, and, in conjunction with the meteorological data base, it is available to model developers to refine existing models or to test new models.